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Getopt::Long(3)        Perl Programmers Reference Guide        Getopt::Long(3)



NAME
       Getopt::Long - Extended processing of command line options

SYNOPSIS
         use Getopt::Long;
         my $data   = "file.dat";
         my $length = 24;
         my $verbose;
         $result = GetOptions ("length=i" => \$length,    # numeric
                               "file=s"   => \$data,      # string
                               "verbose"  => \$verbose);  # flag

DESCRIPTION
       The Getopt::Long module implements an extended getopt function called GetOptions(). This function adheres to
       the POSIX syntax for command line options, with GNU extensions. In general, this means that options have long
       names instead of single letters, and are introduced with a double dash "--". Support for bundling of command
       line options, as was the case with the more traditional single-letter approach, is provided but not enabled by
       default.

Command Line Options, an Introduction
       Command line operated programs traditionally take their arguments from the command line, for example filenames
       or other information that the program needs to know. Besides arguments, these programs often take command line
       options as well. Options are not necessary for the program to work, hence the name 'option', but are used to
       modify its default behaviour. For example, a program could do its job quietly, but with a suitable option it
       could provide verbose information about what it did.

       Command line options come in several flavours. Historically, they are preceded by a single dash "-", and con-
       sist of a single letter.

           -l -a -c

       Usually, these single-character options can be bundled:

           -lac

       Options can have values, the value is placed after the option character. Sometimes with whitespace in between,
       sometimes not:

           -s 24 -s24

       Due to the very cryptic nature of these options, another style was developed that used long names. So instead
       of a cryptic "-l" one could use the more descriptive "--long". To distinguish between a bundle of single-char-
       acter options and a long one, two dashes are used to precede the option name. Early implementations of long
       options used a plus "+" instead. Also, option values could be specified either like

           --size=24

       or

           --size 24

       The "+" form is now obsolete and strongly deprecated.

Getting Started with Getopt::Long
       Getopt::Long is the Perl5 successor of "newgetopt.pl". This was the first Perl module that provided support for
       handling the new style of command line options, hence the name Getopt::Long. This module also supports single-
       character options and bundling. Single character options may be any alphabetic character, a question mark, and
       a dash.  Long options may consist of a series of letters, digits, and dashes.  Although this is currently not
       enforced by Getopt::Long, multiple consecutive dashes are not allowed, and the option name must not end with a
       dash.

       To use Getopt::Long from a Perl program, you must include the following line in your Perl program:

           use Getopt::Long;

       This will load the core of the Getopt::Long module and prepare your program for using it. Most of the actual
       Getopt::Long code is not loaded until you really call one of its functions.

       In the default configuration, options names may be abbreviated to uniqueness, case does not matter, and a sin-
       gle dash is sufficient, even for long option names. Also, options may be placed between non-option arguments.
       See "Configuring Getopt::Long" for more details on how to configure Getopt::Long.

       Simple options

       The most simple options are the ones that take no values. Their mere presence on the command line enables the
       option. Popular examples are:

           --all --verbose --quiet --debug

       Handling simple options is straightforward:

           my $verbose = '';   # option variable with default value (false)
           my $all = '';       # option variable with default value (false)
           GetOptions ('verbose' => \$verbose, 'all' => \$all);

       The call to GetOptions() parses the command line arguments that are present in @ARGV and sets the option vari-
       able to the value 1 if the option did occur on the command line. Otherwise, the option variable is not touched.
       Setting the option value to true is often called enabling the option.

       The option name as specified to the GetOptions() function is called the option specification. Later we'll see
       that this specification can contain more than just the option name. The reference to the variable is called the
       option destination.

       GetOptions() will return a true value if the command line could be processed successfully. Otherwise, it will
       write error messages to STDERR, and return a false result.

       A little bit less simple options

       Getopt::Long supports two useful variants of simple options: negatable options and incremental options.

       A negatable option is specified with an exclamation mark "!" after the option name:

           my $verbose = '';   # option variable with default value (false)
           GetOptions ('verbose!' => \$verbose);

       Now, using "--verbose" on the command line will enable $verbose, as expected. But it is also allowed to use
       "--noverbose", which will disable $verbose by setting its value to 0. Using a suitable default value, the pro-
       gram can find out whether $verbose is false by default, or disabled by using "--noverbose".

       An incremental option is specified with a plus "+" after the option name:

           my $verbose = '';   # option variable with default value (false)
           GetOptions ('verbose+' => \$verbose);

       Using "--verbose" on the command line will increment the value of $verbose. This way the program can keep track
       of how many times the option occurred on the command line. For example, each occurrence of "--verbose" could
       increase the verbosity level of the program.

       Mixing command line option with other arguments

       Usually programs take command line options as well as other arguments, for example, file names. It is good
       practice to always specify the options first, and the other arguments last. Getopt::Long will, however, allow
       the options and arguments to be mixed and 'filter out' all the options before passing the rest of the arguments
       to the program. To stop Getopt::Long from processing further arguments, insert a double dash "--" on the com-
       mand line:

           --size 24 -- --all

       In this example, "--all" will not be treated as an option, but passed to the program unharmed, in @ARGV.

       Options with values

       For options that take values it must be specified whether the option value is required or not, and what kind of
       value the option expects.

       Three kinds of values are supported: integer numbers, floating point numbers, and strings.

       If the option value is required, Getopt::Long will take the command line argument that follows the option and
       assign this to the option variable. If, however, the option value is specified as optional, this will only be
       done if that value does not look like a valid command line option itself.

           my $tag = '';       # option variable with default value
           GetOptions ('tag=s' => \$tag);

       In the option specification, the option name is followed by an equals sign "=" and the letter "s". The equals
       sign indicates that this option requires a value. The letter "s" indicates that this value is an arbitrary
       string. Other possible value types are "i" for integer values, and "f" for floating point values. Using a colon
       ":" instead of the equals sign indicates that the option value is optional. In this case, if no suitable value
       is supplied, string valued options get an empty string '' assigned, while numeric options are set to 0.

       Options with multiple values

       Options sometimes take several values. For example, a program could use multiple directories to search for
       library files:

           --library lib/stdlib --library lib/extlib

       To accomplish this behaviour, simply specify an array reference as the destination for the option:

           GetOptions ("library=s" => \@libfiles);

       Alternatively, you can specify that the option can have multiple values by adding a "@", and pass a scalar ref-
       erence as the destination:

           GetOptions ("library=s@" => \$libfiles);

       Used with the example above, @libfiles (or @$libfiles) would contain two strings upon completion: "lib/srdlib"
       and "lib/extlib", in that order. It is also possible to specify that only integer or floating point numbers are
       acceptable values.

       Often it is useful to allow comma-separated lists of values as well as multiple occurrences of the options.
       This is easy using Perl's split() and join() operators:

           GetOptions ("library=s" => \@libfiles);
           @libfiles = split(/,/,join(',',@libfiles));

       Of course, it is important to choose the right separator string for each purpose.

       Warning: What follows is an experimental feature.

       Options can take multiple values at once, for example

           --coordinates 52.2 16.4 --rgbcolor 255 255 149

       This can be accomplished by adding a repeat specifier to the option specification. Repeat specifiers are very
       similar to the "{...}" repeat specifiers that can be used with regular expression patterns.  For example, the
       above command line would be handled as follows:

           GetOptions('coordinates=f{2}' => \@coor, 'rgbcolor=i{3}' => \@color);

       The destination for the option must be an array or array reference.

       It is also possible to specify the minimal and maximal number of arguments an option takes. "foo=s{2,4}" indi-
       cates an option that takes at least two and at most 4 arguments. "foo=s{,}" indicates one or more values;
       "foo:s{,}" indicates zero or more option values.

       Options with hash values

       If the option destination is a reference to a hash, the option will take, as value, strings of the form
       key"="value. The value will be stored with the specified key in the hash.

           GetOptions ("define=s" => \%defines);

       Alternatively you can use:

           GetOptions ("define=s%" => \$defines);

       When used with command line options:

           --define os=linux --define vendor=redhat

       the hash %defines (or %$defines) will contain two keys, "os" with value ""linux" and "vendor" with value "red-
       hat". It is also possible to specify that only integer or floating point numbers are acceptable values. The
       keys are always taken to be strings.

       User-defined subroutines to handle options

       Ultimate control over what should be done when (actually: each time) an option is encountered on the command
       line can be achieved by designating a reference to a subroutine (or an anonymous subroutine) as the option des-
       tination. When GetOptions() encounters the option, it will call the subroutine with two or three arguments. The
       first argument is the name of the option. For a scalar or array destination, the second argument is the value
       to be stored. For a hash destination, the second arguments is the key to the hash, and the third argument the
       value to be stored. It is up to the subroutine to store the value, or do whatever it thinks is appropriate.

       A trivial application of this mechanism is to implement options that are related to each other. For example:

           my $verbose = '';   # option variable with default value (false)
           GetOptions ('verbose' => \$verbose,
                       'quiet'   => sub { $verbose = 0 });

       Here "--verbose" and "--quiet" control the same variable $verbose, but with opposite values.

       If the subroutine needs to signal an error, it should call die() with the desired error message as its argu-
       ment. GetOptions() will catch the die(), issue the error message, and record that an error result must be
       returned upon completion.

       If the text of the error message starts with an exclamation mark "!"  it is interpreted specially by GetOp-
       tions(). There is currently one special command implemented: "die("!FINISH")" will cause GetOptions() to stop
       processing options, as if it encountered a double dash "--".

       Options with multiple names

       Often it is user friendly to supply alternate mnemonic names for options. For example "--height" could be an
       alternate name for "--length". Alternate names can be included in the option specification, separated by verti-
       cal bar "|" characters. To implement the above example:

           GetOptions ('length|height=f' => \$length);

       The first name is called the primary name, the other names are called aliases. When using a hash to store
       options, the key will always be the primary name.

       Multiple alternate names are possible.

       Case and abbreviations

       Without additional configuration, GetOptions() will ignore the case of option names, and allow the options to
       be abbreviated to uniqueness.

           GetOptions ('length|height=f' => \$length, "head" => \$head);

       This call will allow "--l" and "--L" for the length option, but requires a least "--hea" and "--hei" for the
       head and height options.

       Summary of Option Specifications

       Each option specifier consists of two parts: the name specification and the argument specification.

       The name specification contains the name of the option, optionally followed by a list of alternative names sep-
       arated by vertical bar characters.

           length            option name is "length"
           length|size|l     name is "length", aliases are "size" and "l"

       The argument specification is optional. If omitted, the option is considered boolean, a value of 1 will be
       assigned when the option is used on the command line.

       The argument specification can be

       !   The option does not take an argument and may be negated by prefixing it with "no" or "no-". E.g. "foo!"
           will allow "--foo" (a value of 1 will be assigned) as well as "--nofoo" and "--no-foo" (a value of 0 will
           be assigned). If the option has aliases, this applies to the aliases as well.

           Using negation on a single letter option when bundling is in effect is pointless and will result in a warn-
           ing.

       +   The option does not take an argument and will be incremented by 1 every time it appears on the command
           line. E.g. "more+", when used with "--more --more --more", will increment the value three times, resulting
           in a value of 3 (provided it was 0 or undefined at first).

           The "+" specifier is ignored if the option destination is not a scalar.

       = type [ desttype ] [ repeat ]
           The option requires an argument of the given type. Supported types are:

           s   String. An arbitrary sequence of characters. It is valid for the argument to start with "-" or "--".

           i   Integer. An optional leading plus or minus sign, followed by a sequence of digits.

           o   Extended integer, Perl style. This can be either an optional leading plus or minus sign, followed by a
               sequence of digits, or an octal string (a zero, optionally followed by '0', '1', .. '7'), or a hexadec-
               imal string ("0x" followed by '0' .. '9', 'a' .. 'f', case insensitive), or a binary string ("0b" fol-
               lowed by a series of '0' and '1').

           f   Real number. For example 3.14, "-6.23E24" and so on.

           The desttype can be "@" or "%" to specify that the option is list or a hash valued. This is only needed
           when the destination for the option value is not otherwise specified. It should be omitted when not needed.

           The repeat specifies the number of values this option takes per occurrence on the command line. It has the
           format "{" [ min ] [ "," [ max ] ] "}".

           min denotes the minimal number of arguments. It defaults to 1 for options with "=" and to 0 for options
           with ":", see below. Note that min overrules the "=" / ":" semantics.

           max denotes the maximum number of arguments. It must be at least min. If max is omitted, but the comma is
           not, there is no upper bound to the number of argument values taken.

       : type [ desttype ]
           Like "=", but designates the argument as optional.  If omitted, an empty string will be assigned to string
           values options, and the value zero to numeric options.

           Note that if a string argument starts with "-" or "--", it will be considered an option on itself.

       : number [ desttype ]
           Like ":i", but if the value is omitted, the number will be assigned.

       : + [ desttype ]
           Like ":i", but if the value is omitted, the current value for the option will be incremented.

Advanced Possibilities
       Object oriented interface

       Getopt::Long can be used in an object oriented way as well:

           use Getopt::Long;
           $p = new Getopt::Long::Parser;
           $p->configure(...configuration options...);
           if ($p->getoptions(...options descriptions...)) ...

       Configuration options can be passed to the constructor:

           $p = new Getopt::Long::Parser
                    config => [...configuration options...];

       Thread Safety

       Getopt::Long is thread safe when using ithreads as of Perl 5.8.  It is not thread safe when using the older
       (experimental and now obsolete) threads implementation that was added to Perl 5.005.

       Documentation and help texts

       Getopt::Long encourages the use of Pod::Usage to produce help messages. For example:

           use Getopt::Long;
           use Pod::Usage;

           my $man = 0;
           my $help = 0;

           GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
           pod2usage(1) if $help;
           pod2usage(-exitstatus => 0, -verbose => 2) if $man;

           __END__

           =head1 NAME

           sample - Using Getopt::Long and Pod::Usage

           =head1 SYNOPSIS

           sample [options] [file ...]

            Options:
              -help            brief help message
              -man             full documentation

           =head1 OPTIONS

           =over 8

           =item B<-help>

           Print a brief help message and exits.

           =item B<-man>

           Prints the manual page and exits.

           =back

           =head1 DESCRIPTION

           B<This program> will read the given input file(s) and do something
           useful with the contents thereof.

           =cut

       See Pod::Usage for details.

       Storing option values in a hash

       Sometimes, for example when there are a lot of options, having a separate variable for each of them can be cum-
       bersome. GetOptions() supports, as an alternative mechanism, storing options in a hash.

       To obtain this, a reference to a hash must be passed as the first argument to GetOptions(). For each option
       that is specified on the command line, the option value will be stored in the hash with the option name as key.
       Options that are not actually used on the command line will not be put in the hash, on other words,
       "exists($h{option})" (or defined()) can be used to test if an option was used. The drawback is that warnings
       will be issued if the program runs under "use strict" and uses $h{option} without testing with exists() or
       defined() first.

           my %h = ();
           GetOptions (\%h, 'length=i');       # will store in $h{length}

       For options that take list or hash values, it is necessary to indicate this by appending an "@" or "%" sign
       after the type:

           GetOptions (\%h, 'colours=s@');     # will push to @{$h{colours}}

       To make things more complicated, the hash may contain references to the actual destinations, for example:

           my $len = 0;
           my %h = ('length' => \$len);
           GetOptions (\%h, 'length=i');       # will store in $len

       This example is fully equivalent with:

           my $len = 0;
           GetOptions ('length=i' => \$len);   # will store in $len

       Any mixture is possible. For example, the most frequently used options could be stored in variables while all
       other options get stored in the hash:

           my $verbose = 0;                    # frequently referred
           my $debug = 0;                      # frequently referred
           my %h = ('verbose' => \$verbose, 'debug' => \$debug);
           GetOptions (\%h, 'verbose', 'debug', 'filter', 'size=i');
           if ( $verbose ) { ... }
           if ( exists $h{filter} ) { ... option 'filter' was specified ... }

       Bundling

       With bundling it is possible to set several single-character options at once. For example if "a", "v" and "x"
       are all valid options,

           -vax

       would set all three.

       Getopt::Long supports two levels of bundling. To enable bundling, a call to Getopt::Long::Configure is
       required.

       The first level of bundling can be enabled with:

           Getopt::Long::Configure ("bundling");

       Configured this way, single-character options can be bundled but long options must always start with a double
       dash "--" to avoid ambiguity. For example, when "vax", "a", "v" and "x" are all valid options,

           -vax

       would set "a", "v" and "x", but

           --vax

       would set "vax".

       The second level of bundling lifts this restriction. It can be enabled with:

           Getopt::Long::Configure ("bundling_override");

       Now, "-vax" would set the option "vax".

       When any level of bundling is enabled, option values may be inserted in the bundle. For example:

           -h24w80

       is equivalent to

           -h 24 -w 80

       When configured for bundling, single-character options are matched case sensitive while long options are
       matched case insensitive. To have the single-character options matched case insensitive as well, use:

           Getopt::Long::Configure ("bundling", "ignorecase_always");

       It goes without saying that bundling can be quite confusing.

       The lonesome dash

       Normally, a lone dash "-" on the command line will not be considered an option. Option processing will termi-
       nate (unless "permute" is configured) and the dash will be left in @ARGV.

       It is possible to get special treatment for a lone dash. This can be achieved by adding an option specification
       with an empty name, for example:

           GetOptions ('' => \$stdio);

       A lone dash on the command line will now be a legal option, and using it will set variable $stdio.

       Argument callback

       A special option 'name' "<>" can be used to designate a subroutine to handle non-option arguments. When GetOp-
       tions() encounters an argument that does not look like an option, it will immediately call this subroutine and
       passes it one parameter: the argument name.

       For example:

           my $width = 80;
           sub process { ... }
           GetOptions ('width=i' => \$width, '<>' => \&process);

       When applied to the following command line:

           arg1 --width=72 arg2 --width=60 arg3

       This will call "process("arg1")" while $width is 80, "process("arg2")" while $width is 72, and "pro-
       cess("arg3")" while $width is 60.

       This feature requires configuration option permute, see section "Configuring Getopt::Long".

Configuring Getopt::Long
       Getopt::Long can be configured by calling subroutine Getopt::Long::Configure(). This subroutine takes a list of
       quoted strings, each specifying a configuration option to be enabled, e.g.  "ignore_case", or disabled, e.g.
       "no_ignore_case". Case does not matter. Multiple calls to Configure() are possible.

       Alternatively, as of version 2.24, the configuration options may be passed together with the "use" statement:

           use Getopt::Long qw(:config no_ignore_case bundling);

       The following options are available:

       default     This option causes all configuration options to be reset to their default values.

       posix_default
                   This option causes all configuration options to be reset to their default values as if the environ-
                   ment variable POSIXLY_CORRECT had been set.

       auto_abbrev Allow option names to be abbreviated to uniqueness.  Default is enabled unless environment variable
                   POSIXLY_CORRECT has been set, in which case "auto_abbrev" is disabled.

       getopt_compat
                   Allow "+" to start options.  Default is enabled unless environment variable POSIXLY_CORRECT has
                   been set, in which case "getopt_compat" is disabled.

       gnu_compat  "gnu_compat" controls whether "--opt=" is allowed, and what it should do. Without "gnu_compat",
                   "--opt=" gives an error. With "gnu_compat", "--opt=" will give option "opt" and empty value.  This
                   is the way GNU getopt_long() does it.

       gnu_getopt  This is a short way of setting "gnu_compat" "bundling" "permute" "no_getopt_compat". With
                   "gnu_getopt", command line handling should be fully compatible with GNU getopt_long().

       require_order
                   Whether command line arguments are allowed to be mixed with options.  Default is disabled unless
                   environment variable POSIXLY_CORRECT has been set, in which case "require_order" is enabled.

                   See also "permute", which is the opposite of "require_order".

       permute     Whether command line arguments are allowed to be mixed with options.  Default is enabled unless
                   environment variable POSIXLY_CORRECT has been set, in which case "permute" is disabled.  Note that
                   "permute" is the opposite of "require_order".

                   If "permute" is enabled, this means that

                       --foo arg1 --bar arg2 arg3

                   is equivalent to

                       --foo --bar arg1 arg2 arg3

                   If an argument callback routine is specified, @ARGV will always be empty upon successful return of
                   GetOptions() since all options have been processed. The only exception is when "--" is used:

                       --foo arg1 --bar arg2 -- arg3

                   This will call the callback routine for arg1 and arg2, and then terminate GetOptions() leaving
                   "arg2" in @ARGV.

                   If "require_order" is enabled, options processing terminates when the first non-option is encoun-
                   tered.

                       --foo arg1 --bar arg2 arg3

                   is equivalent to

                       --foo -- arg1 --bar arg2 arg3

                   If "pass_through" is also enabled, options processing will terminate at the first unrecognized
                   option, or non-option, whichever comes first.

       bundling (default: disabled)
                   Enabling this option will allow single-character options to be bundled. To distinguish bundles from
                   long option names, long options must be introduced with "--" and bundles with "-".

                   Note that, if you have options "a", "l" and "all", and auto_abbrev enabled, possible arguments and
                   option settings are:

                       using argument               sets option(s)
                       ------------------------------------------
                       -a, --a                      a
                       -l, --l                      l
                       -al, -la, -ala, -all,...     a, l
                       --al, --all                  all

                   The surprising part is that "--a" sets option "a" (due to auto completion), not "all".

                   Note: disabling "bundling" also disables "bundling_override".

       bundling_override (default: disabled)
                   If "bundling_override" is enabled, bundling is enabled as with "bundling" but now long option names
                   override option bundles.

                   Note: disabling "bundling_override" also disables "bundling".

                   Note: Using option bundling can easily lead to unexpected results, especially when mixing long
                   options and bundles. Caveat emptor.

       ignore_case  (default: enabled)
                   If enabled, case is ignored when matching long option names. If, however, bundling is enabled as
                   well, single character options will be treated case-sensitive.

                   With "ignore_case", option specifications for options that only differ in case, e.g., "foo" and
                   "Foo", will be flagged as duplicates.

                   Note: disabling "ignore_case" also disables "ignore_case_always".

       ignore_case_always (default: disabled)
                   When bundling is in effect, case is ignored on single-character options also.

                   Note: disabling "ignore_case_always" also disables "ignore_case".

       auto_version (default:disabled)
                   Automatically provide support for the --version option if the application did not specify a handler
                   for this option itself.

                   Getopt::Long will provide a standard version message that includes the program name, its version
                   (if $main::VERSION is defined), and the versions of Getopt::Long and Perl. The message will be
                   written to standard output and processing will terminate.

                   "auto_version" will be enabled if the calling program explicitly specified a version number higher
                   than 2.32 in the "use" or "require" statement.

       auto_help (default:disabled)
                   Automatically provide support for the --help and -? options if the application did not specify a
                   handler for this option itself.

                   Getopt::Long will provide a help message using module Pod::Usage. The message, derived from the
                   SYNOPSIS POD section, will be written to standard output and processing will terminate.

                   "auto_help" will be enabled if the calling program explicitly specified a version number higher
                   than 2.32 in the "use" or "require" statement.

       pass_through (default: disabled)
                   Options that are unknown, ambiguous or supplied with an invalid option value are passed through in
                   @ARGV instead of being flagged as errors. This makes it possible to write wrapper scripts that pro-
                   cess only part of the user supplied command line arguments, and pass the remaining options to some
                   other program.

                   If "require_order" is enabled, options processing will terminate at the first unrecognized option,
                   or non-option, whichever comes first.  However, if "permute" is enabled instead, results can become
                   confusing.

                   Note that the options terminator (default "--"), if present, will also be passed through in @ARGV.

       prefix      The string that starts options. If a constant string is not sufficient, see "prefix_pattern".

       prefix_pattern
                   A Perl pattern that identifies the strings that introduce options.  Default is "--|-|\+" unless
                   environment variable POSIXLY_CORRECT has been set, in which case it is "--|-".

       long_prefix_pattern
                   A Perl pattern that allows the disambiguation of long and short prefixes. Default is "--".

                   Typically you only need to set this if you are using nonstandard prefixes and want some or all of
                   them to have the same semantics as '--' does under normal circumstances.

                   For example, setting prefix_pattern to "--|-|\+|\/" and long_prefix_pattern to "--|\/" would add
                   Win32 style argument handling.

       debug (default: disabled)
                   Enable debugging output.

Exportable Methods
       VersionMessage
           This subroutine provides a standard version message. Its argument can be:

           *   A string containing the text of a message to print before printing the standard message.

           *   A numeric value corresponding to the desired exit status.

           *   A reference to a hash.

           If more than one argument is given then the entire argument list is assumed to be a hash.  If a hash is
           supplied (either as a reference or as a list) it should contain one or more elements with the following
           keys:

           "-message"
           "-msg"
               The text of a message to print immediately prior to printing the program's usage message.

           "-exitval"
               The desired exit status to pass to the exit() function.  This should be an integer, or else the string
               "NOEXIT" to indicate that control should simply be returned without terminating the invoking process.

           "-output"
               A reference to a filehandle, or the pathname of a file to which the usage message should be written.
               The default is "\*STDERR" unless the exit value is less than 2 (in which case the default is "\*STD-
               OUT").

           You cannot tie this routine directly to an option, e.g.:

               GetOptions("version" => \&VersionMessage);

           Use this instead:

               GetOptions("version" => sub { VersionMessage() });

       HelpMessage
           This subroutine produces a standard help message, derived from the program's POD section SYNOPSIS using
           Pod::Usage. It takes the same arguments as VersionMessage(). In particular, you cannot tie it directly to
           an option, e.g.:

               GetOptions("help" => \&HelpMessage);

           Use this instead:

               GetOptions("help" => sub { HelpMessage() });

Return values and Errors
       Configuration errors and errors in the option definitions are signalled using die() and will terminate the
       calling program unless the call to Getopt::Long::GetOptions() was embedded in "eval { ...  }", or die() was
       trapped using $SIG{__DIE__}.

       GetOptions returns true to indicate success.  It returns false when the function detected one or more errors
       during option parsing. These errors are signalled using warn() and can be trapped with $SIG{__WARN__}.

Legacy
       The earliest development of "newgetopt.pl" started in 1990, with Perl version 4. As a result, its development,
       and the development of Getopt::Long, has gone through several stages. Since backward compatibility has always
       been extremely important, the current version of Getopt::Long still supports a lot of constructs that nowadays
       are no longer necessary or otherwise unwanted. This section describes briefly some of these 'features'.

       Default destinations

       When no destination is specified for an option, GetOptions will store the resultant value in a global variable
       named "opt_"XXX, where XXX is the primary name of this option. When a progam executes under "use strict" (rec-
       ommended), these variables must be pre-declared with our() or "use vars".

           our $opt_length = 0;
           GetOptions ('length=i');    # will store in $opt_length

       To yield a usable Perl variable, characters that are not part of the syntax for variables are translated to
       underscores. For example, "--fpp-struct-return" will set the variable $opt_fpp_struct_return. Note that this
       variable resides in the namespace of the calling program, not necessarily "main". For example:

           GetOptions ("size=i", "sizes=i@");

       with command line "-size 10 -sizes 24 -sizes 48" will perform the equivalent of the assignments

           $opt_size = 10;
           @opt_sizes = (24, 48);

       Alternative option starters

       A string of alternative option starter characters may be passed as the first argument (or the first argument
       after a leading hash reference argument).

           my $len = 0;
           GetOptions ('/', 'length=i' => $len);

       Now the command line may look like:

           /length 24 -- arg

       Note that to terminate options processing still requires a double dash "--".

       GetOptions() will not interpret a leading "<>" as option starters if the next argument is a reference. To force
       "<" and ">" as option starters, use "><". Confusing? Well, using a starter argument is strongly deprecated any-
       way.

       Configuration variables

       Previous versions of Getopt::Long used variables for the purpose of configuring. Although manipulating these
       variables still work, it is strongly encouraged to use the "Configure" routine that was introduced in version
       2.17. Besides, it is much easier.

Trouble Shooting
       GetOptions does not return a false result when an option is not supplied

       That's why they're called 'options'.

       GetOptions does not split the command line correctly

       The command line is not split by GetOptions, but by the command line interpreter (CLI). On Unix, this is the
       shell. On Windows, it is COMMAND.COM or CMD.EXE. Other operating systems have other CLIs.

       It is important to know that these CLIs may behave different when the command line contains special characters,
       in particular quotes or backslashes. For example, with Unix shells you can use single quotes ("'") and double
       quotes (""") to group words together. The following alternatives are equivalent on Unix:

           "two words"
           'two words'
           two\ words

       In case of doubt, insert the following statement in front of your Perl program:

           print STDERR (join("|",@ARGV),"\n");

       to verify how your CLI passes the arguments to the program.

       Undefined subroutine &main::GetOptions called

       Are you running Windows, and did you write

           use GetOpt::Long;

       (note the capital 'O')?

       How do I put a "-?" option into a Getopt::Long?

       You can only obtain this using an alias, and Getopt::Long of at least version 2.13.

           use Getopt::Long;
           GetOptions ("help|?");    # -help and -? will both set $opt_help

AUTHOR
       Johan Vromans <jvromansATsquirrel.nl>

COPYRIGHT AND DISCLAIMER
       This program is Copyright 1990,2005 by Johan Vromans.  This program is free software; you can redistribute it
       and/or modify it under the terms of the Perl Artistic License or the GNU General Public License as published by
       the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
       implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
       for more details.

       If you do not have a copy of the GNU General Public License write to the Free Software Foundation, Inc., 675
       Mass Ave, Cambridge, MA 02139, USA.



perl v5.8.8                       2001-09-21                   Getopt::Long(3)